MARINE MOLLUSCA OF THE UNITED STATES. Ill 



Genus CHAMA, Linnteus. 

 Syst. Nat., edit. x. 1758. 



1. C. ARCiNELLA, Liiiiifeus. Fig. 459, 402, 463. 



Syst. Nat., edit. xii. 1139. 1767. 



Shell heart-shaped, with a large depressed lunule beneath the 

 umbones, both valves radiately ribbed, the ri])s spinous, and the 

 interstices punctured; margins ver}^ finely crenulated. White or 

 yellowish, most frequently stained with pink-red. 



North Carolina to West Indies. 



The spines are generally only partially developed. 



2. C. MACROPHYLLA, Chemnitz. Fig. 460. 



Conch. Cab., vii. 149, t. 52, f. 514, 515. 1784. 



Shell ovate, both valves lamellated throughout, lamelloj imbri- 

 cated, large, irregular, striated ; margins of the valves very 

 minutely crenulated; color bright yellow, whitish witliiu. 



North Carolina to West Indies. 



Family ARCAD.E. 



Animal with the mantle open ; foot large, bent, and deeply 

 grooved ; gills very oblique, united posteriorly to a membranous 

 septum. 



Synopsis of Oenera, 



Shell equivalveor nearly so, oval or subquadrate, veutricosc, strongly nl)bed 

 or caucellated ; margins smooth or dentated, close or siuuated veutrally ; 

 hinge straight, teeth very numerous, transverse ; umboues anterior, 

 separated by a flat, lozenge-shaped ligamcntal area, with numerous 

 cartilage-grooves. Akca, Linn. 



Shell orbicular, nearly equilateral, smooth, or radiately striated ; umboues 

 central, divided by a striated ligamental area ; liinge with a semicircular 

 row of transverse teeth ; margins crenate within. 



Pectuncult:s, Lam. 



Shell trigonal, with the umbones turned towards the short posterior side ; 

 smooth or sculptured ; epidermis olive, interior pearly., margins crenu- 

 lated ; liinge with a prominent internal cartilage-pit, and a series of sharp 

 teeth on each side. Nucula, Lam. 



Shell oblong, rounded in front, produced and pointed behind ; margin not 

 crenated; pallial line with a small sinus ; teeth as in Niicula. 



Leda, Schum. 

 12 



